The present invention relates to a method and an apparatus for position-sensorless motor control in which a rotor position of a motor is detected without a position sensor, whereby the driving of the motor is controlled, in particular, when the rotor is at a stop or slowly revolves.
A brushless motor does not have a mechanical commutation element such as a brush, but instead has an electric circuit for carrying out the commutation electrically. The electric circuit controls the currents flowing through stator windings, in synchronization with the rotor revolution.
A brushless motor comprises a permanent magnet and thus at least two magnetic poles. A rotor position is defined by an angle around the center axis of a rotor between the direction (d-axis direction) of the center axis of a magnetic pole of the rotor and a reference direction (xcex1-axis direction) fixed to a stator.
Electric commutation needs detection of rotor position. A prior art motor control apparatus for brushless motor has obtained the information on rotor position using a position sensor such as Hall devices, a resolver, a magnetic encoder, and an optical encoder. However, the position sensor has caused a higher cost and a larger size in the prior art brushless motor.
In a position-sensorless motor control apparatus (prior art example, hereafter) disclosed in Japanese Laid-Open Patent Publication No. Hei 10-323099, a rotor position is detected without an above-described position sensor. Thus, the cost and the size of a brushless motor are reduced.
The prior art example detects a rotor position without a position sensor and controls the driving of motor, especially when a rotor is at a stop and slowly revolves, according to the following steps:
(1) Estimating the rotor position, thereby estimating the d-axis direction and the q-axis direction (xcex3-axis direction and xcex4-axis direction, respectively) of the rotor based on the estimated rotor position. Here, the q-axis direction is defined as the direction advancing by 90xc2x0 in terms of electric angle from the d-axis direction in the direction of the rotor revolution.
(2) Superimposing a predetermined current signal or voltage signal for rotor position estimation (rotor-position estimation current/voltage signal, hereafter) on the xcex3-axis direction component of a target current vector or a target voltage vector of the stator windings. Here, a target current vector of the stator windings is a vector representing target currents in the control over the currents flowing through the stator windings. A target voltage vector of the stator windings is a vector representing target voltages in the control over the voltages applied across the stator windings. In the invention, a target current vector with superimposed wave means a vector representing the target currents on which are superimposed the rotor-position estimation current signal. A target voltage vector with superimposed wave means a vector representing the target voltages that are superimposed the rotor-position estimation voltage signal on.
(3) Converting the target current vector with superimposed wave into the corresponding target voltage vector of the stator windings. A motor driver supplies electric power based on either the target voltage vector of the stator windings or the target voltage vector with superimposed wave, to the stator windings. In particular, in a pulse width modulation (PWM) control over the currents of the stator windings, the motor driver modulates the target voltages represented by either the target voltage vector of the stator windings or the target voltage vector with superimposed wave, through the PWM, and then applies the modulated target voltages across the stator windings. Electric power corresponding to the rotor-position estimation current/voltage signal is applied to the stator windings through the power supplied to the stator windings by the motor drive. Here, the rotor-position estimation current/voltage signal is, for example, an AC signal having a constant period equal to a multiple of the PWM carrier period and a constant amplitude. Each of the rotor-position estimation current/voltage signals is generally referred to as a rotor-position estimation signal hereafter, when distinction between both of the signals is unnecessary. In the above-described PWM control, a constant AC power corresponding to the rotor-position estimation signal is applied to the stator windings. Then, a current response to the AC power is generated in the stator windings.
(4) Detecting the above-described current response in the xcex4-axis direction at a predetermined phase. For example, a sampling of the current response is carried out at each peak of the rotor-position estimation signal, that is, at each half period of the rotor-position estimation signal.
(5) Correcting the estimated rotor position so that the detected current response approaches zero in the xcex4-axis direction.
These steps (1) through (5) are repeated during the driving control of the motor.
The amount of deviation of the xcex4-axis direction from the d-axis direction is designated as xcex94 xcex8, equal to the amount of deviation of the xcex4-axis direction from the q-axis direction, and hereafter referred to as a position estimation error. The amplitude of the current response in the xcex4-axis direction is substantially proportional to sin (2xcex94 xcex8). Accordingly, the estimated rotor position and the actual rotor position coincide with each other within a predetermined error, when the current response converge to zero within a predetermined error in the xcex4-axis direction.
The prior art position-sensorless motor control uses the rotor-position estimation signal with a constant frequency. In particular, the constant frequency falls within the audio-frequency band from a few tens Hz to a few hundreds Hz. As a result, when the stator teeth and the like vibrate in synchronization with the rotor-position estimation signal, an undesired sound is generated. The undesired sound is large especially near the frequency of the rotor-position estimation signal.
The prior art position-sensorless motor control uses the rotor-position estimation signal with a constant amplitude. Accordingly, the current response to the rotor-position estimation signal has a substantially constant amplitude. On the other hand, the larger the amplitudes of the currents flowing through the stator windings becomes, the larger an electric noise, which is hereafter referred to as a noise, in the xcex4-axis direction is generally generated, and hence, the greater the ratio (S/N ratio) of the current response""s amplitude to the noise is reduced. When the S/N ratio is small, the distinction between the current response and the noise is difficult, and hence, the position estimation error is large. Furthermore, in the prior art position-sensorless motor control, the sampling of the current response is carried out only at each half period of the rotor-position estimation signal, and thus, the number of the samples is small. Accordingly, the position estimation error may be very large in the prior art, when the S/N ratios of the respective samples of the current response are small.
In order to suppress the position estimation error, the S/N ratios of the current response have to increase. To do this, the amplitude of the rotor-position estimation signal may be increased, or the noise may be reduced. However, an increasing of the amplitude of the rotor-position estimation signal is difficult, since the above-described undesired sound is large when the amplitude of the rotor-position estimation signal is large. On the other hand, in order to reduce the noise in the current response, the current response may be sufficiently attenuated through a low pass filter (LPF). Alternatively, a gain may be reduced in a process of calculating the correction of the estimated position from the position estimation error. However, these approaches may delay the estimation of the rotor position, thereby slowing down the response in the driving control of motor. Thus, in the prior art position-sensorless motor control, the control over the noise degrades the controllability over the motor. In other words, the prior art has low noise immunity.
An object of the present invention is to provide a method and an apparatus for position-sensorless motor control for reducing an undesired sound and at the same time, increasing the S/N ratio of the detection of a current response to a rotor-position estimation signal without control delay, that is, having high noise immunity, especially when a rotor is at a stop and slowly revolves
According to an aspect of the invention, a position-sensorless motor control method comprises the steps of:
(A) determining a target current vector of stator windings;
(B) setting one of a rotor-position estimation current signal and a rotor-position estimation voltage signal, with varying the period thereof;
(C) detecting currents flowing through the stator windings;
(D) carrying out one of
(a) superimposing the rotor-position estimation current signal on a component of the target current vector in a first direction based on an estimated position (xcex3-axis direction, hereafter) of a rotor, thereby obtaining a target current vector with superimposed wave, and
(b) superimposing the rotor-position estimation voltage signal on a component of a target voltage vector corresponding to the target current vector in the first direction, thereby obtaining a target voltage vector with superimposed wave;
(E) supplying electric power to the stator windings through a motor driving device on the basis of one of the target current vector with superimposed wave and the target voltage vector with superimposed wave;
(F) measuring a current response to one of the rotor-position estimation current signal and the rotor-position estimation voltage signal, from a component of a current vector in a second direction having a fixed relation with the first direction, the current vector representing the currents detected in the detecting step; and
(G) correcting the xcex3-axis direction on the basis of the current response.
Each of the rotor-position estimation current signal and the rotor-position estimation voltage signal is generally referred to as a rotor-position estimation signal hereafter, when the distinction between both of the signals is unnecessary.
In the above-described method for position-sensorless motor control, which is hereafter referred to as sensorless control method, the period of the rotor-position estimation signal is not constant but varying. Accordingly, the vibration of the stator teeth and the like in synchronization with the rotor-position estimation signal does not have a constant frequency, and then, a sound caused by the vibration does not have a constant frequency. Therefore, the sound is prevented from growing too loud, since the vibration and the sound are not amplified owing to the varying of the frequency. Thus, the sensorless control reduces an undesired sound caused by the superimposing of the rotor-position estimation signal. Furthermore, the amplitude of the rotor-position estimation signal can be increased without a large undesired sound in contrast to the prior art.
In the sensorless control method, the period of the rotor-position estimation signal may vary at random. Then, the period of the rotor-position estimation signal has no correlation before and after the variation, thereby permitting a further reduction of the undesired sound.
In the sensorless control method, the period of the rotor-position estimation signal may vary on the basis of a predetermined table. When the values in the table are arranged in the order of the variation of the period of the rotor-position estimation signal, these values may be selected at random or in a manner that the difference between the values before and after the variation exceeds a predetermined value. Alternatively, the table may be a list of random numbers or predetermined parameters, and then, a simple operation using the table value may vary the period at random or in a manner that the difference exceeds a predetermined value. In each case of the above-described table value arrangement, the period of the rotor-position estimation signal may vary such as to reduce the undesired sound. In addition, the determination of the period of the rotor-position estimation signal is carried out by means of table reference and hence does not need a complicated operation, thereby reducing the operation time. As a result, loads on a CPU and similar devices in a control circuit are reduced.
According to another aspect of the invention, a position-sensorless motor control method comprises the steps of:
(A) determining a target current vector of stator windings;
(B) setting one of a rotor-position estimation current signal and a rotor-position estimation voltage signal, with varying the amplitude thereof;
(C) detecting currents flowing through the stator windings;
(D) carrying out one of
(a) superimposing the rotor-position estimation current signal on a component of the target current vector in a first direction based on a xcex3-axis direction of a rotor, thereby obtaining a target current vector with superimposed wave, and
(b) superimposing the rotor-position estimation voltage signal on a component of a target voltage vector corresponding to the target current vector in the first direction, thereby obtaining a target voltage vector with superimposed wave;
(E) supplying electric power to the stator windings through a motor driving device on the basis of one of the target current vector with superimposed wave and the target voltage vector with superimposed wave;
(F) measuring a current response to one of the rotor-position estimation current signal and the rotor-position estimation voltage signal, from a component of a current vector in a second direction having a fixed relation with the first direction, the current vector representing the currents detected in the detecting step; and
(G) correcting the xcex3-axis direction on the basis of the current response.
In the above-described sensorless control method, the amplitude of the rotor-position estimation signal varies. In particular, the variation of the amplitude may correspond to the variation of the amplitudes of the currents flowing through the stator windings. By virtue of the correspondence, the amplitude of the rotor-position estimation signal can be controlled depending on the noise intensity in the currents of the stator windings, thereby being adjusted to a level not to degrade the S/N ratio of the current response detection. Accordingly, the amplitude of the current response to the rotor-position estimation signal is prevented from increasing to excess in comparison with the currents of the stator windings. As a result, the undesired sound caused by the superimposing of the rotor-position estimation signals is reduced in contrast to the prior art.
In the sensorless control method, when the amplitudes of the currents of the stator windings increase, the amplitude of the rotor-position estimation signal may be increased. The reason is as follows: The larger the amplitudes of the currents of the stator windings are, the larger a noise in the current response is. Accordingly, when the amplitudes of the currents of the stator windings increase, the amplitude of the rotor-position estimation signal is increased, thereby being prevent from increasing to excess in comparison with the currents of the stator windings. As a result, in the driving control of the motor, the undesired sound caused by the superimposing of the rotor-position estimation signal is reduced as a whole, in contrast to the prior art. At the same time, the S/N ratio of the current response detection is maintained at a sufficiently high level.
In the sensorless control method, either the detected currents of the stator windings or the target currents thereof may determine the increasing of the currents of the stator windings.
According to still another aspect of the invention, a position-sensorless motor control method comprises the steps of:
(A) determining a target current vector of stator windings;
(B) setting one of a rotor-position estimation current signal and a rotor-position estimation voltage signal, with a predetermined period;
(C) detecting currents flowing through the stator windings;
(D) carrying out one of
(a) superimposing the rotor-position estimation current signal on a component of the target current vector in a first direction based on a xcex3-axis direction of a rotor, thereby obtaining a target current vector with superimposed wave, and
(b) superimposing the rotor-position estimation voltage signal on a component of a target voltage vector corresponding to the target current vector in the first direction, thereby obtaining a target voltage vector with superimposed wave;
(E) supplying electric power to the stator windings through a motor driving device on the basis of one of the target current vector with superimposed wave and the target voltage vector with superimposed wave;
(F) measuring a current response to one of the rotor-position estimation current signal and the rotor-position estimation voltage signal, from a component of a current vector in a second direction having a fixed relation with the first direction through sampling at least three times in each period of one of the rotor-position estimation current signal and the rotor-position estimation voltage signal, the current vector representing the currents detected in the detecting step; and
(G) correcting the xcex3-axis direction on the basis of the current response.
In the above-described sensorless control method, the number of the samples of the current response is large in contrast to the prior art, in which the current response is sampled at each half period of the rotor-position estimation signal. A large number of the samples improve the S/N ratio of the current response detection in contrast to the prior art.
The sampling of the current response may be carried out plural times in each half period of the rotor-position estimation signal. Then, a larger number of the samples of the current response are obtained. Furthermore, especially when the waveform of the rotor-position estimation signal is symmetric with respect to the middle point between the former half and the latter half of the period, the positions of the sampling can be arranged symmetrically with respect to the middle point between the former half and the latter half of the period of the current response. Using this symmetry, noises in the samples of the current response can be canceled out between the mutually corresponding samples through, for example, averaging with each other. The cancellation improves the S/N ratio of the current response detection.
According to a further aspect of the invention, a position-sensorless motor control method comprises the steps of:
(A) determining a target current vector of stator windings;
(B) setting one of a rotor-position estimation current signal and a rotor-position estimation voltage signal, wherein (a) the period thereof is an even multiple of a carrier period of PWM and (b) the waveform thereof is symmetric with respect to the middle point between the former half and the latter half of the period;
(C) detecting currents flowing through the stator windings;
(D) carrying out one of
(a) superimposing the rotor-position estimation current signal on a component of the target current vector in a first direction based on a xcex3-axis direction of a rotor, thereby obtaining a target current vector with superimposed wave, and
(b) superimposing the rotor-position estimation voltage signal on a component of a target voltage vector corresponding to the target current vector in the first direction, thereby obtaining a target voltage vector with superimposed wave;
(E) (a) modulating target voltages through the PWM, the target voltages represented by one of a target voltage vector corresponding to the target current vector with superimposed wave and the target voltage vector with superimposed wave, and (b) applying the modulated target voltages across the stator windings through a motor driving device;
(F) measuring a current response to one of the rotor-position estimation current signal and the rotor-position estimation voltage signal, from a component of a current vector in a second direction having a fixed relation with the first direction, on the basis of the symmetric waveform of one of the rotor-position estimation current signal and the rotor-position estimation voltage signal, the current vector representing the currents detected in the detecting step; and
(G) correcting the xcex3-axis direction on the basis of the current response.
When a motor driver comprises, for example, an inverter, thereby performing a PWM control, the waveforms of the currents flowing through the stator windings generally have a distortion with a period substantially equal to the PWM carrier period in comparison with the ideally smooth waveforms. Similarly, the waveform of the current response to the rotor-position estimation signal also has a distortion with a period substantially equal to the PWM carrier period. In the above-described sensorless control method, the period of the rotor-position estimation signal is an even multiple of the PWM carrier period and the waveform thereof is symmetric with respect to the middle point between the former half and the latter half of the period. Accordingly, the distortion in the waveform of the rotor-position estimation signal is substantially symmetric with respect to the middle point between the former half and the latter half of a period. Therefore, the waveform of the current response with the distortion caused by the PWM has similar symmetry. Using this symmetry, the current response detecting error caused by the above-described distortion can be reduced. For example, the sampling of the current response is carried out symmetrically with respect to the middle point between the former half and the latter half of the period. More specifically, for a constant sampling frequency, the frequency of the rotor-position estimation signal is set to be an even multiple of the sampling frequency, and the sampling positions are arranged symmetrically with respect to the middle point of one period of the rotor-position estimation signal. Then, noises in the samples can be canceled out between the samples at the mutually symmetric positions through, for example, averaging with each other.
A PWM control by the motor driver is implemented in each of the sensorless control methods according to the above-described aspects of the invention, as follows:
(A) (a) the period of one of the rotor-position estimation current signal and the rotor-position estimation voltage signal is set to be an even multiple of a carrier period of PWM and (b) the waveform thereof is set symmetrically with respect to the middle point between the former half and the latter half of the period;
(B) target voltages are modulated through the PWM, the target voltages represented by one of a target voltage vector corresponding to the target current vector with superimposed wave and the target voltage vector with superimposed wave, and the modulated target voltages are applied across the stator windings through the motor driving device; and
(C) the current response is measured on the basis of the symmetric waveform of one of the rotor-position estimation current signal and the rotor-position estimation voltage signal.
Thus, each of the sensorless control methods according to the above-described aspects of the invention is applicable when the motor driver performs the PWM control.
According to a still further aspect of the invention, a position-sensorless motor control method comprises the steps of:
(A) determining a target current vector of stator windings;
(B) setting one of a rotor-position estimation current signal and a rotor-position estimation voltage signal, with a predetermined period;
(C) detecting currents flowing through the stator windings;
(D) carrying out one of
(a) superimposing the rotor-position estimation current signal on a component of the target current vector in a first direction based on a xcex3-axis direction of a rotor, thereby obtaining a target current vector with superimposed wave, and
(b) superimposing the rotor-position estimation voltage signal on a component of a target voltage vector corresponding to the target current vector in the first direction, thereby obtaining a target voltage vector with superimposed wave;
(E) supplying electric power to the stator windings through a motor driving device on the basis of one of the target current vector with superimposed wave and the target voltage vector with superimposed wave;
(F) (a) multiplying a component of a current vector in a second direction orthogonal to the first direction in terms of electric angle by a signal, the current vector representing the currents detected in the detecting step, the signal having (1) a period substantially equal to the period of one of the rotor-position estimation current signal and the rotor-position estimation voltage signal, and (2) a phase substantially shifted by 90xc2x0 in terms of electric angle from one of the rotor-position estimation current signal and the rotor-position estimation voltage signal, and
(b) measuring a current response to one of the rotor-position estimation current signal and the rotor-position estimation voltage signal from the result of the multiplication; and
(G) correcting the xcex3-axis direction on the basis of the current response.
The current response has a period equal to that of the rotor-position estimation signal and a phase shifted by 90xc2x0 from the signal, in the second direction, namely, the orthogonal direction in terms of electric angle to the direction of the superimposing of the rotor-position estimation signal. Accordingly, the currents flowing through the stator windings are detected, and the second direction component of a current vector, which represents the detected currents, is multiplied by the above-described signal. Then, the current response can be measured from the result of the multiplication.
For example, when the rotor-position estimation signal is a sinusoidal wave, the above-described result of the multiplication is integrated over one period of the rotor-position estimation signal. Then, a Fourier coefficient corresponding to the period of the rotor-position estimation signal is obtained among the Fourier coefficients contained in the second direction component of the current vector, which represents the detected currents flowing through the stator windings. The Fourier coefficient is substantially equal to the amplitude of the current response. Furthermore, noises in the detected currents of the stator windings are suppressed through the integration, whereby the error is reduced in the amplitude of the current response in contrast to the prior art.
According to another aspect of the invention different from the above-described aspect, a position-sensorless motor control method comprises the steps of:
(A) determining a target current vector of stator windings;
(B) setting one of a rotor-position estimation current signal and a rotor-position estimation voltage signal;
(C) detecting currents flowing through the stator windings;
(D) carrying out one of
(a) superimposing the rotor-position estimation current signal on a component of the target current vector in a first direction based on a xcex3-axis direction of a rotor, thereby obtaining a target current vector with superimposed wave, and
(b) superimposing the rotor-position estimation voltage signal on a component of a target voltage vector corresponding to the target current vector in the first direction, thereby obtaining a target voltage vector with superimposed wave;
(E) supplying electric power to the stator windings through a motor driving device on the basis of one of the target current vector with superimposed wave and the target voltage vector with superimposed wave;
(F) measuring a current response to one of the rotor-position estimation current signal and the rotor-position estimation voltage signal, from a component of a current vector in a second direction having a fixed relation with the first direction, the current vector representing the currents detected in the detecting step;
(G) limiting a value of the current response; and
(H) correcting the xcex3-axis direction on the basis of the current response with the value limited in the limiting step.
The current response may abruptly enlarge because of a noise therein. Then, the limiter limits the current response. Accordingly, a detection of an excessively large current response is prevented from disturbing the driving control of the motor.
The larger the current response is, the larger the detecting error thereof is. Accordingly, when the current response exceeds a certain level, the estimated rotor position is replaced with a constant value, instead of the correction of the estimated rotor position on the basis of the detected value of the current response. As a result, the estimation error is reduced as a whole.
In the above-described sensorless control methods according to the invention, preferably, (a) the first direction is one of the xcex3-axis direction and a direction substantially shifted by 90xc2x0 in terms of electric angle from the xcex3-axis direction; (b) the second direction is a direction substantially shifted by 90xc2x0 in terms of electric angle from the first direction; and (c) the xcex3-axis direction is corrected so that the current response in the second direction substantially converges to zero.
For example, the amplitude of the current response in the xcex4-axis direction component of the current vector, which represents the detected currents of the stator windings, is substantially proportional to sin (2xcex94xcex8), when the rotor-position estimation current/voltage signal is superimposed on the xcex3-axis direction component of the target current/voltage vector. Here, the position estimation error of the rotor in the d-axis direction, namely, the deviation of the xcex3-axis direction from the d-axis direction is denoted by xcex94xcex8. Accordingly, the xcex3-axis direction may be controlled so as to coincide with the d-axis direction, if the amplitude of the current response is controlled so as to shrink to zero in the xcex4-axis direction.
According to an aspect of the invention, a position-sensorless motor control apparatus comprises:
(A) a motor controlling section for determining a target current vector of stator windings;
(B) a superimposed wave generating section for setting one of a rotor-position estimation current signal and a rotor-position estimation voltage signal, with varying the period thereof;
(C) current detecting devices for detecting currents flowing through the stator windings;
(D) a current controlling section for carrying out one of
(a) superimposing the rotor-position estimation current signal on a component of the target current vector in a first direction based on a xcex3-axis direction of a rotor, thereby obtaining a target current vector with superimposed wave, and further calculating a corresponding target voltage vector; and
(b) a current controlling section for superimposing the rotor-position estimation voltage signal on a component of a target voltage vector corresponding to the target current vector in the first direction, thereby obtaining a target voltage vector with superimposed wave;
(E) a motor driving device for supplying electric power to the stator windings on the basis of one of the target voltage vector corresponding to the target current vector with superimposed wave and the target voltage vector with superimposed wave; and
(F) a rotor-position estimating section for
(a) measuring a current response to one of the rotor-position estimation current signal and the rotor-position estimation voltage signal, from a component of a current vector in a second direction having a fixed relation with the first direction, the current vector representing the currents detected by the current detecting devices, and
(b) correcting the xcex3-axis direction on the basis of the current response.
In the above-described apparatus for position-sensorless motor control, which is hereafter referred to as sensorless control apparatus, the period of the rotor-position estimation signal is not constant but varying. Accordingly, a vibration of the stator teeth and the like in synchronization with the rotor-position estimation signal does not have a constant frequency, and then, a sound caused by the vibration does not have a constant frequency. Therefore, the sound is prevented from growing too loud, since the vibration and the sound are not amplified owing to the varying of the frequency. Thus, the sensorless control reduces an undesired sound caused by the superimposing of the rotor-position estimation signal. Furthermore, the amplitude of the rotor-position estimation signal can be increased without a large undesired sound in contrast to the prior art.
In the sensorless control apparatus, the superimposed wave generating section may vary the period of the rotor-position estimation signal at random. Then, the period of the rotor-position estimation signal has no correlation before and after the variation, thereby permitting a further reduction in the undesired sound.
In the sensorless control apparatus, the superimposed wave generating section may comprise a memory storing a predetermined table, whereby the period of the rotor-position estimation signal may vary on the basis of the table. When the values in the table are arranged in the order of the variation of the period of the rotor-position estimation signal, these values may be selected at random or in a manner that the difference between the values before and after the variation exceeds a predetermined value. Alternatively, the table may be a list of random numbers or predetermined parameters. Then, by a simple operation using the table value, the period may vary at random or in a manner that the difference exceeds a predetermined value. In each case of the above-described table value arrangement, the period of the rotor-position estimation signal may vary such as to reduce the undesired sound. In addition, the determination of the period of the rotor-position estimation signal is carried out by means of table reference and hence does not need a complicated operation, thereby reducing the operation time. As a result, loads on a CPU and similar devices in a control circuit are reduced.
According to another aspect of the invention, a position-sensorless motor control apparatus comprises:
(A) a motor controlling section for determining a target current vector of stator windings;
(B) a superimposed wave generating section for setting one of a rotor-position estimation current signal and a rotor-position estimation voltage signal, with varying the amplitude thereof;
(C) current detecting devices for detecting currents flowing through the stator windings;
(D) a current controlling section for carrying out one of
(a) superimposing the rotor-position estimation current signal on a component of the target current vector in a first direction based on a xcex3-axis direction of a rotor, thereby obtaining a target current vector with superimposed wave, and further calculating a corresponding target voltage vector, and
(b) superimposing the rotor-position estimation voltage signal on a component of a target voltage vector corresponding to the target current vector in the first direction, thereby obtaining a target voltage vector with superimposed wave;
(E) a motor driving device for supplying electric power to the stator windings on the basis of one of the target voltage vector corresponding to the target current vector with superimposed wave and the target voltage vector with superimposed wave; and
(F) a rotor-position estimating section for
(a) measuring a current response to one of the rotor-position estimation current signal and the rotor-position estimation voltage signal, from a component of a current vector in a second direction having a fixed relation with the first direction, the current vector representing the currents detected by the current detecting devices, and
(b) correcting the xcex3-axis direction on the basis of the current response.
In the above-described sensorless control apparatus, the amplitude of the rotor-position estimation signal varies. In particular, the variation of the amplitude may correspond to the variation of the amplitudes of the currents flowing through the stator windings. By virtue of the correspondence, the amplitude of the rotor-position estimation signal can be controlled depending on the noise intensity in the currents of the stator windings, thereby being adjusted to a level not to degrade the S/N ratio of the current response detection. Accordingly, the amplitude of the current response to the rotor-position estimation signal is prevented from increasing to excess in comparison with the currents of the stator windings. As a result, an undesired sound caused by the superimposing of the rotor-position estimation signals is reduced in contrast to the prior art.
In the sensorless control apparatus, when the amplitudes of the currents of the stator windings increase, the superimposed wave generating section may increase the amplitude of the rotor-position estimation signal. The reason is as follows: The larger the amplitudes of the currents of the stator windings are, the larger a noise in the current response is. Accordingly, when the amplitudes of the currents of the stator windings increase, the amplitude of the rotor-position estimation signal is increased. As a result, in the driving control of the motor, the undesired sound caused by the superimposing of the rotor-position estimation signal is reduced as a whole, in contrast to the prior art. At the same time, the S/N ratio of the current response detection is maintained at a sufficiently high level.
In the above-described sensorless control apparatus, either the detected currents of the stator windings or the target currents thereof may determine the increasing of the currents of the stator windings.
According to still another aspect of the invention, a position-sensorless motor control apparatus comprises:
(A) a motor controlling section for determining a target current vector of stator windings;
(B) a superimposed wave generating section for setting one of a rotor-position estimation current signal and a rotor-position estimation voltage signal, with a predetermined period;
(C) current detecting devices for detecting currents flowing through the stator windings;
(D) a current controlling section for carrying out one of
(a) superimposing the rotor-position estimation current signal on a component of the target current vector in a first direction based on a xcex3-axis direction of a rotor, thereby obtaining a target current vector with superimposed wave, and further calculating a corresponding target voltage vector, and
(b) superimposing the rotor-position estimation voltage signal on a component of a target voltage vector corresponding to the target current vector in the first direction, thereby obtaining a target voltage vector with superimposed wave;
(E) a motor driving device for supplying electric power to the stator windings on the basis of one of the target voltage vector corresponding to the target current vector with superimposed wave and the target voltage vector with superimposed wave; and
(F) a rotor-position estimating section for
(a) measuring a current response to one of the rotor-position estimation current signal and the rotor-position estimation voltage signal, from a component of a current vector in a second direction having a fixed relation with the first direction through sampling at least three times in each period of one of the rotor-position estimation current signal and the rotor-position estimation voltage signal, the current vector representing the currents detected by the current detecting devices, and
(b) correcting the xcex3-axis direction on the basis of the current response.
In the sensorless control apparatus, the number of the samples of the current response is larger in contrast to the prior art, in which the current response is sampled at each half period of the rotor-position estimation signal. A large number of the samples improve the S/N ratio of the current response detection in contrast to the prior art.
The rotor-position estimating section may sample the current response plural times in each half period of the rotor-position estimation signal. Then, a larger number of the samples of the current response are obtained. Furthermore, especially when the waveform of the rotor-position estimation signal is symmetric with respect to the middle point between the former half and the latter half of the period, the positions of the sampling can be arranged symmetrically with respect to the middle point between the former half and the latter half of the period of the current response. Using this symmetry, noises in the samples of the current response can be canceled out between the mutually corresponding samples through, for example, averaging with each other. The cancellation improves the S/N ratio of the current response detection.
According to a further aspect of the invention, a position-sensorless motor control apparatus comprises:
(A) a motor controlling section determining a target current vector of stator windings;
(B) a superimposed wave generating section for setting one of a rotor-position estimation current signal and a rotor-position estimation voltage signal, with the period thereof being an even multiple of the carrier period of PWM and the waveform thereof symmetric with respect to the middle point between the former half and the latter half of the period;
(C) current detecting devices for detecting currents flowing through the stator windings;
(D) a current controlling section for carrying out one of
(a) superimposing the rotor-position estimation current signal on a component of the target current vector in a first direction based on a xcex3-axis direction of a rotor, thereby obtaining a target current vector with superimposed wave, and further calculating a corresponding target voltage vector, and
(b) superimposing the rotor-position estimation voltage signal on a component of a target voltage vector corresponding to the target current vector in the first direction, thereby obtaining a target voltage vector with superimposed wave;
(E) a motor driving device for modulating target voltages through the PWM, the target voltages represented by one of the target voltage vector corresponding to the target current vector with superimposed wave and the target voltage vector with superimposed wave, and applying the modulated target voltages across the stator windings; and
(F) a rotor-position estimating section for
(a) measuring a current response to one of the rotor-position estimation current signal and the rotor-position estimation voltage signal, from a component of a current vector in a second direction having a fixed relation with the first direction, on the basis of the symmetric waveform of one of the rotor-position estimation current signal and the rotor-position estimation voltage signal, the current vector representing the currents detected by the current detecting devices, and
(b) correcting the xcex3-axis direction on the basis of the current response.
A motor driving device comprises, for example, an inverter, thereby performing a PWM control. In the PWM control, the waveforms of the currents flowing through the stator windings generally have a distortion with a period substantially equal to the PWM carrier period in comparison with the ideally smooth waveforms. Similarly, the waveform of the current response to the rotor-position estimation signal also has a distortion with a period substantially equal to the PWM carrier period. In the above-described sensorless control apparatus, the superimposed wave generating section sets the period of the rotor-position estimation signal to be an even multiple of the PWM carrier period, and the waveform thereof to be symmetric with respect to the middle point between the former half and the latter half of the period. Accordingly, the distortion in the waveform of the rotor-position estimation signal is substantially symmetric with respect to the middle point between the former half and the latter half of a period. Therefore, the waveform of the current response with the distortion caused by the PWM has similar symmetry. Using this symmetry, the rotor-position estimating section reduces the current response detecting error caused by the above-described distortion. For example, the section carries out the sampling of the current response symmetrically with respect to the middle point between the former half and the latter half of the period. More specifically, for a constant sampling frequency, the section sets the frequency of the rotor-position estimation signal to be an even multiple of the sampling frequency, and arranges the sampling positions symmetrically with respect to the middle point of one period of the rotor-position estimation signal. Then, the section can canceled out noises in the samples between the samples in the mutually symmetric positions through, for example, averaging with each other.
A PWM control by a motor driving device can be implemented in each of the sensorless control apparatus according to the above-described aspects of the invention, as follows:
(A) the superimposed wave generating section sets (a) the period of one of the rotor-position estimation current signal and the rotor-position estimation voltage signal to be an even multiple of the carrier period of PWM, and (b) the waveform thereof to be symmetric with respect to the middle point between the former half and the latter half of the period;
(B) the motor driving device modulates target voltages through the PWM, the target voltages represented by one of the target voltage vector corresponding to the target current vector with superimposed wave and the target voltage vector with superimposed wave, and applies the modulated target voltages across the stator windings; and
(C) the rotor-position estimating section measures the current response on the basis of the symmetric waveform of one of the rotor-position estimation current signal and the rotor-position estimation voltage signal.
Thus, the motor driving device can perform the PWM control in each of the sensorless control apparatus according to the above-described aspects of the invention.
According to a still further aspect of the invention, a position-sensorless motor control apparatus comprises:
(A) a motor controlling section for determining a target current vector of stator windings;
(B) a superimposed wave generating section for setting one of a rotor-position estimation current signal and a rotor-position estimation voltage signal, with a predetermined period;
(C) current detecting devices for detecting currents flowing through the stator windings;
(D) a current controlling section for carrying out one of
(a) superimposing the rotor-position estimation current signal on a component of the target current vector in a first direction based on a xcex3-axis direction of a rotor, thereby obtaining a target current vector with superimposed wave, and calculating a corresponding target voltage vector, and
(b) superimposing the rotor-position estimation voltage signal on a component of a target voltage vector corresponding to the target current vector in the first direction, thereby obtaining a target voltage vector with superimposed wave;
(E) a motor driving device for supplying electric power to the stator windings on the basis of one of the target voltage vector corresponding to the target current vector with superimposed wave and the target voltage vector with superimposed wave; and
(F) a rotor-position estimating section for
(a) multiplying a component of a current vector in a second direction orthogonal to the first direction in terms of electric angle by a signal, the current vector representing the currents detected by the current detecting devices, the signal having (1) a period substantially equal to the period of one of the rotor-position estimation current signal and the rotor-position estimation voltage signal, and (2) a phase substantially shifted by 90xc2x0 in terms of electric angle from one of the rotor-position estimation current signal and the rotor-position estimation voltage signal,
(b) measuring a current response to one of the rotor-position estimation current signal and the rotor-position estimation voltage signal, from the result of the multiplication, and
(c) correcting the xcex3-axis direction on the basis of the current response.
The current response has a period equal to that of the rotor-position estimation signal and a phase shifted by 90xc2x0 from the signal in the second direction, namely, the orthogonal direction in terms of electric angle to the direction of the superimposing of the rotor-position estimation signal. Accordingly, the currents flowing through the stator windings are detected, and the second direction component of a current vector, which represents the detected currents, is multiplied by the above-described signal. Then, the current response can be measured from the result of the multiplication.
For example, when the rotor-position estimation signal is a sinusoidal wave, the above-described result of the multiplication is integrated over one period of the rotor-position estimation signal. Then, a Fourier coefficient corresponding to the period of the rotor-position estimation signal is obtained among the Fourier coefficients contained in the second direction component of the current vector, which represents the detected currents flowing through the stator windings. The Fourier coefficient is substantially equal to the amplitude of the current response. Furthermore, noise in the detected currents of the stator windings is suppressed through the integration, whereby the error is reduced in the amplitude of the current response in contrast to the prior art.
According to another aspect of the invention, a position-sensorless motor control apparatus comprises:
(A) a motor controlling section for determining a target current vector of stator windings;
(B) a superimposed wave generating section for setting one of a rotor-position estimation current signal and a rotor-position estimation voltage signal;
(C) current detecting devices for detecting currents flowing through the stator windings;
(D) a current controlling section for carrying out one of
(a) superimposing the rotor-position estimation current signal on a component of the target current vector in a first direction based on a xcex3-axis direction of a rotor, thereby obtaining a target current vector with superimposed wave, and further calculating a corresponding target voltage vector, and
(b) superimposing the rotor-position estimation voltage signal on a component of a target voltage vector corresponding to the target current vector in the first direction, thereby obtaining a target voltage vector with superimposed wave;
(E) a motor driving device for supplying electric power to the stator windings on the basis of one of the target voltage vector corresponding to the target current vector with superimposed wave and the target voltages with superimposed wave; and
(F) a rotor-position estimating section having a limiter, the rotor-position estimating section for
(a) measuring a current response to one of the rotor-position estimation current signal and the rotor-position estimation voltage signal, from a component of a current vector in a second direction having a fixed relation with the first direction,
(b) limiting a value of the current response using the limiter, and
(c) correcting the xcex3-axis direction on the basis of the current response with the value limited by the limiter.
The current response may abruptly enlarge because of a noise therein. Then, the limiter limits the current response. Accordingly, a detection of an excessively large current response is prevented from disturbing the driving control of the motor.
The larger the current response is, the larger the detecting error thereof is. Accordingly, when the current response exceeds a certain level, the estimated rotor position is replaced with a constant value, instead of the correction of the estimated rotor position on the basis of the detected value of the current response. As a result, the estimation error is reduced as a whole.
In the above described sensorless control apparatus according to the invention:
(A) the current controlling section sets the first direction to be one of the xcex3-axis direction and a direction substantially shifted by 90xc2x0 in terms of electric angle from the xcex3-axis direction; and
(B) the rotor-position estimating section sets the second direction to be a direction substantially shifted by 90xc2x0 in terms of electric angle from the first direction, and corrects the xcex3-axis direction so that the current response in the second direction substantially converges to zero.
For example, the amplitude of the current response in the xcex4-axis direction component of the current vector, which represents the detected currents of the stator windings, is substantially proportional to sin (2xcex94xcex8), when the rotor-position estimation current/voltage signal is superimposed on the xcex3-axis direction component of the target current/voltage vector. Here, the position estimation error of the rotor in the d-axis direction, namely, the deviation of the xcex3-axis direction from the d-axis direction is denoted by xcex94xcex8. Accordingly, the xcex4-axis direction may be controlled so as to coincide with the d-axis direction, if the amplitude of the current response is controlled so as to shrink to zero in the xcex4-axis direction.
An electric vehicle according to the invention comprises a wheel driving motor with an above-described position-sensorless motor control apparatus according to the invention. Large sound caused by the wheel driving motor is undesired since it makes persons in the cabin uncomfortable. Furthermore, delay in the driving control of the wheel driving motor is undesired since it degrades the running performance of the electric vehicle. As described above, the sensorless control apparatus according to the invention can reduce the undesired sound with maintaining the driving controllability, especially when the wheel driving motor is at start up and slowly runs. Accordingly, in the above-described electric vehicle at starting and in slow moving, the driving control of the wheel driving motor is smooth, and the undesired sound is soft. Thus, the electric vehicle makes persons in the cabin comfortable during the running.
A fan according to the invention comprises a fan driving motor with an above-described position-sensorless motor control apparatus according to the invention. Large sound caused by the fan of a ventilator is, for example, undesired since it makes persons in a room uncomfortable under ventilation. Furthermore, delay in the driving control of the fan driving motor is undesired since it degrades the ventilation performance. As described above, the sensorless control apparatus according to the invention can reduce the undesired sound with maintaining the drive controllability, especially when the fan driving motor is at start up and slowly runs. Accordingly, in the above-described fan, the driving control of the fan driving motor is smooth, and the undesired sound is soft. Thus, the fan used in a ventilator, for example, is prevented from making persons in the room uncomfortable under ventilation.
A refrigerator according to the invention comprises a compressor with an above-described position-sensorless motor control apparatus according to the invention. Large sound caused by the compressor of the refrigerator is undesired especially at bedtime. Furthermore, delay in the driving control of the compressor is undesired since it degrades the cooling performance of the refrigerator. As described above, the sensorless control apparatus according to the invention can reduce the undesired sound with maintaining the drive controllability, especially when the compressor is at start up and slowly runs. Accordingly, in the above-described refrigerator at starting and in normal driving, the driving control of the compressor is smooth and the undesired sound is soft. Thus, the refrigerator is prevented from, for example, disturbing comfortable sleep in home at night.
An air conditioner according to the invention comprises a compressor provided with an above-described position-sensorless motor control apparatus according to the invention. Large sound generated by the compressor of the air conditioner is undesired since it makes persons in a room and the neighbors outside the room uncomfortable. Furthermore, delay in the driving control of the compressor is undesired since it degrades the air-conditioning performance of the air conditioner. As described above, the sensorless control apparatus according to the invention can reduce the undesired sound with maintaining the drive controllability especially when the compressor is at start up and slowly runs. Accordingly, in the above-described air conditioner, at starting and in normal driving, the driving control of the compressor is smooth and the undesired sound is soft. Thus, the air conditioner is prevented from making persons in the room and the neighbors outside the room uncomfortable.
While the novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings.